WebM is an audiovisual media file format.[3]
It is primarily intended to offer a royalty-free alternative to use in the HTML5 video and the HTML5 audio elements. It has a sister project WebP for images. The development of the format is sponsored by Google, and the corresponding software is distributed under a BSD license.

VLC media player,[19]MPlayer and K-Multimedia Player have native support for playing WebM files.[20]FFmpeg can encode and decode VP8 videos when built with support for libvpx, the VP8/VP9 codec library of the WebM project, as well as mux/demux WebM-compliant files.[21] On July 23, 2010 Fiona Glaser, Ronald Bultje, and David Conrad of the FFmpeg team announced the ffvp8 decoder. Their testing found that ffvp8 was faster than Google's own libvpx decoder.[22][23]MKVToolNix, the popular Matroska creation tools, implemented support for multiplexing/demultiplexing WebM-compliant files out of the box.[24] Haali Media Splitter also announced support for muxing/demuxing of WebM.[24] Since version 1.4.9, the LiVES video editor has support for realtime decoding and for encoding to WebM format using ffmpeg libraries.

MPC-HC since build SVN 2071 supports WebM playback with internal VP8 decoder based on FFmpeg's code.[22][25] The full decoding support for WebM is available in MPC-HC since version 1 April 2499.0.[26]

On January 7, 2011, Rockchip released the world's first chip to host a full hardware implementation of 1080p VP8 decoding. The video acceleration in the RK29xx chip is handled by the WebM Project's G-Series 1 hardware decoder IP.[43]

In June 2011, ZiiLABS demonstrated their 1080p VP8 decoder implementation running on the ZMS-20 processor. The chip's programmable media processing array is used to provide the VP8 acceleration.[44]

Also ST-Ericsson and Huawei have hardware implementations in their computer chips.[45]

The original WebM license terminated both patent grants and copyright redistribution terms if a patent infringement lawsuit was filed, causing concerns around GPL compatibility.
In response to those concerns, the WebM Project decoupled the patent grant from the copyright grant, offering the code under a standard BSD license and patents under a separate grant.[46] The Free Software Foundation, which maintains the Free Software Definition, has given its endorsement for WebM and VP8[47] and considers the software's license to be compatible with the GNU General Public License.[48][49] On January 19, 2011, the Free Software Foundation announced its official support for the WebM project.[50] In February 2011, Microsoft's Vice President of Internet Explorer called upon Google to provide indemnification against patent suits.[51]

Although Google has irrevocably released all of its patents on VP8 as a royalty-free format,[52] the MPEG LA, licensors of the H.264 patent pool, have expressed interest in creating a patent pool for VP8.[53][54] Conversely, other researchers cite evidence that On2 made a particular effort to avoid any MPEG LA patents.[55] As a result of the threat, the United States Department of Justice (DOJ) started an investigation in March 2011 into the MPEG LA for its role in possibly attempting to stifle competition.[56][57] In March 2013, MPEG LA announced that it had reached an agreement with Google to license patents that "may be essential" for the implementation of the VP8 codec, and give Google the right to sub-license these patents to any third-party user of VP8 or VP9.[58][59]

In March 2013, Nokia filed an objection to the Internet Engineering Task Force concerning Google's proposal for the VP8 codec to be a core part of WebM, saying it holds essential patents to VP8's implementation.[60] Nokia listed 64 patents and 22 pending applications, adding it was not prepared to license any of them for VP8.[61] On August 5, 2013, a court in Mannheim, Germany, ruled that VP8 does not infringe a patent owned and asserted by Nokia.[62]

^ ab"WebM FAQ". May 19, 2010. WebM is an open media file format designed for the web. WebM files consist of video streams compressed with the VP8 video codec and audio streams compressed with the Vorbis audio codec. The WebM file structure is based on the Matroska media container.

^Mills, Chris (May 19, 2010). "Opera supports the WebM video format". Dev.Opera. Opera Software ASA. Retrieved March 8, 2011. On the day of the announcement, Opera released an experimental WebM-enabled build. This feature is now part of the core functionality of Opera 10.60 and all of our future desktop browser releases.